1. Field of Invention
The present invention relates to a liquid crystal device, a method for manufacturing the same, and an electronic device equipped with the liquid crystal device. More particularly, the invention relates to a technique of placing spacers between a pair of substances.
2. Description of Related Art
Related art liquid crystal devices can be constructed such that a lower substrate and an upper substrate are bonded together with a seal member in the respective peripheries of the substrates, and a liquid crystal layer is sealed between the pair of substrates. The related art also places spacers, such as resin balls, glass balls, or columnar resin members, between the pair of substrates in order to keep the substrate spacing evenly in the substrate surfaces.
In general, such liquid crystal devices are manufactured by the following process steps of: depositing electrodes and alignment layers on each of the lower substrate and the upper substrate; printing an uncured seal member on the periphery of, for example, the lower substrate with an opening serving as a liquid crystal inlet formed therein; spraying spacers on the surface of the substrate or the other substrate; and bonding the lower substrate and the upper substrate together through a seal member, thereby forming a hollow liquid crystal cell. Then, curing the uncured seal member; injecting a liquid crystal into the liquid crystal cell through the liquid crystal inlet that is formed in the seal member in advance, by vacuum injection; sealing the inlet with a seal member; and finally, bonding an optical film, such as a retardation film or a polarizer, on the outer surfaces of the lower substrate and the upper substrate, thereby forming a liquid crystal device.
For the spacer spraying step for example, a method can be used in which spacers are evenly sprayed on the substrate by spraying a spacer dispersion liquid in which spacers are dispersed in a prescribed solvent. On the other hand, for example, a technique of arranging spacers in a specific region in a liquid crystal cell by ink jetting (droplet discharge method) is disclosed in Japanese Unexamined Patent Application Publication No. 2001-188235. The spacers act to keep the substrate spacing evenly, whereas they exert a negative influence on display, for example, they cause light leakage and misalignment of a liquid crystal when arranged in a pixel region. Therefore, liquid crystal devices in which spacers are selectively arranged only in a non-pixel region in a liquid crystal cell, and a method for manufacturing the same is disclosed in Japanese Unexamined Patent Application Publication Nos. 54-107754 and 2-308224. For example, Japanese Unexamined Patent Application Publication No. 9-105946 discloses a method of placing spacers in a non-pixel region by ink jetting. Another example is a specific spacer fixed-point placement device by ink jetting, as disclosed in Japanese Unexamined Patent Application Publication No. 2002-72218.
As described above, the related art includes methods of arranging spacers in a non-pixel region which is not involved directly in display. Although it is necessary to arrange a predetermined number of spacers or more in the liquid crystal cell in view of keeping the substrate spacing evenly, it is preferable to place a reduced or minimum number of spacers needed in consideration of a bad influence on display. From the above viewpoint, the related art techniques give no consideration to a beneficial or the optimum number (density) of spacers at all. Accordingly, a standard of a beneficial or the optimum number (density) of spacers has been required to reduce uneven display due to uneven cell thickness (substrate spacing) in the substrate surface and a decrease in contrast due to light leakage owing to the presence of spacers and misalignment and so on, thereby enhancing display quality.
It has also been required to provide a method of stably controlling the number of spacers by ink jetting. Specifically, the ink jetting only emits ink (liquid). However, in order to emit a dispersion liquid that contains a solid matter, such as a spacer, only in a fixed region, the diameter of the nozzle of the ink jet unit must be optimized. However, there has been no indicator for the most suitable nozzle diameter for the spacer dispersion liquid.
The present invention addresses the above and/or other circumstances, and provides a liquid crystal device that is superior in display quality by providing a beneficial or optimized number (density) of spacers in arranging the spacers in fixed points in a substrate surface with a droplet discharge unit, such as an ink jet unit, a method for manufacturing the liquid crystal device, and an electronic device including the liquid crystal device.
According to a first exemplary embodiment of the present invention, a liquid crystal device is provided in which a pair of substrates is opposed to each other through a seal member and a liquid crystal and spacers are contained in a sealed space enclosed with the pair of substrates and the seal member. The spacers are placed on all or part of intersection points of a plurality of first parallel phantom lines extending in a first direction and a plurality of second parallel phantom lines extending in a second direction different from the first direction with the spacers arranged separately, in aggregation, or in a mixture thereof. The density of spacers is from 50 to 300/mm2 and the average number of spacers on all the intersection points is from 0.2 to 3.
According to the invention, the density of spacers is from 50 to 300/mm2 and the average number of spacers on all the intersection points of the first phantom lines and the second phantom lines is from 0.2 to 3. Accordingly, deterioration in display quality due to the spacers can be sufficiently reduced so that display quality can be enhanced.
The liquid crystal device of the invention is manufactured by the below-described method such that the spacers are placed on all or part of intersection points of a plurality of first parallel phantom lines extending in a first direction and a plurality of second parallel phantom lines extending in a second direction different from the first direction with the spacers arranged separately, in aggregation, or a mixture thereof. Specifically, according to the method for manufacturing the liquid crystal device of the present invention, a spacer dispersion liquid having the spacers dispersed in a predetermined solvent is dropped on the substrate with a droplet discharge unit, and each droplet contains a random number of spacers. The solvent is evaporated after dropping, so that the spacers are left on the substrate. Since the droplet discharge unit is used, the spacers are not irregularly arranged on the substrate but are separately arranged on the intersection points of the plurality of first parallel phantom lines extending in a first direction corresponding to an arrangement direction of nozzles of the droplet discharge unit and the plurality of second parallel phantom lines extending in the second direction corresponding to a scanning direction of the nozzles of the droplet discharge unit. In the invention, the reason why the spacers are placed on all or part of the intersection points is because the number of spacers contained in the droplet is random and relatively small, so that even when droplet was dropped, it may contain no spacer, finally some points may contain no spacer.
The base for the above numerical range is described below via Examples. When the density of spacers becomes smaller than 50/mm2, the substrate spacing cannot be sufficiently kept by the spacers, so that unevenness in cell thickness is increased to significantly decrease display quality. On the other hand, when the density of spacers becomes larger than 300/mm2, bubbles generate in a liquid crystal at low temperature, causing a failure called vacuum bubbles. This is because, since a liquid crystal has a higher thermal expansion coefficient than that of spacers, vacuum portions occur locally in the liquid crystal layer at low temperature; however, when there are too many spacers, the substrates cannot follow to curve inward, so that the vacuum portions remain.
When the average number of spacers at all the intersection points of the first and second phantom lines is smaller than 0.2, points having no spacer increase excessively to cause variation in the arrangement of the spacers and to increase unevenness of cell thickness, so that display quality is significantly decreased. On the other hand, when the number is larger than three, spacer aggregates increase excessively to cause unevenness of cell thickness and light leakage, thus significantly decreasing display quality.
The spacers may be arranged in a non-pixel region. Specifically, the presence of spacers in display region causes mis-orientation of the liquid crystal and light leakage, thus significantly decreasing display quality. Therefore, arranging the spacers in a non-pixel region that is not involved directly in display significantly enhances display quality.
As described above, arranging the spacers in a non-pixel region enhances display quality. Furthermore, providing a light-shielding layer corresponding to the non-pixel region reduces or prevents display failure, such as light leakage more reliably.
The spacers may be colored. For example, when the liquid crystal device is used as a display, light sometimes leaks from the arranged spacers to cause white display (light display) during black display (dark display). However, coloring the spacers, as described above, particularly using black colored spacers allows black display (dark display) reliably.
The surfaces of the spacers may be subjected to a process of controlling the orientation of the liquid crystal. Specifically, irregular orientation of a liquid crystal sometimes occurs in the vicinity of the surfaces of the spacers to decrease contrast. However, providing a device to control the orientation on the surfaces of the spacers allows the orientation of the liquid crystal also on the surfaces of the spacers. This reduces or prevents occurrence of light leakage, and thus provides a liquid crystal device that seldom produces problems, such as deterioration in contrast. An example of the orientation control means includes a surface treatment that applies a long-chain alkyl group to the surface of the spacers with a silane coupling agent or the like.
The surfaces of the spacers may include a bonding layer to bond the spacers themselves onto the substrates. An example of the material for the bonding layer may include a thermosetting resin. The thermosetting resin is thus formed on the surfaces of the spacers, for example, after spacers has been arranged in certain positions between the substrates, they are subjected to heat treatment, so that the spacers can be stably fixed to the substrates, and thus the occurrence of problems such that the spacers float out of positions can be reduced or prevented.
Among the three structures of the structure in which the spacers are colored, the structure in which the surfaces of the spacers are subjected to a process of controlling the orientation of the liquid crystal, and the structure in which the surfaces of the spacers include a bonding layer for bonding the spacers themselves onto the substrate, one spacer may have one structure, two structure, or all of the three structures.
According to a second exemplary embodiment of the invention, there is provided a method for manufacturing a liquid crystal device in which a pair of substrates is opposed to each other through a seal member and a liquid crystal and spacers are contained in a sealed space enclosed with the pair of substrates and the seal member. The method includes: dropping a spacer dispersion liquid having the spacers dispersed in a predetermined solvent in certain positions on one of the pair of substrates with a droplet discharge unit; and placing the spacers by evaporating the solvent in droplets dropped on the substrate so as to arrange the spacers on all or part of the intersection points of a plurality of first parallel phantom lines extending in a first direction and a plurality of second parallel phantom lines extending in a second direction different from the first direction, with the spacers arranged separately, in aggregation, or in mixture thereof, the density of spacers being from 50 to 300/mm2 and the average number of spacers on all the intersection points being from 0.2 to 3.
Specifically, after a spacer dispersion liquid having the spacers dispersed in a predetermined solvent has been dropped in certain positions on the substrate with a droplet discharge unit, the solvent in droplets is evaporated, thereby arranging the spacers in fixed points on the substrate. At that time, the density and the average number of spacers contained in one droplet are limited as described above, so that a liquid crystal device with high display quality can be provided. As described above, the first direction in which the first phantom lines extend corresponds to the direction of arrangement of the droplet discharge nozzles of the droplet discharge unit. The second direction in which the second phantom lines extend corresponds to the scanning direction of the droplet discharge nozzles of the droplet discharge unit.
The diameter of the droplet discharge nozzles of the droplet discharge unit is preferably at least 10 xcexcm and at most 100 xcexcm and, more preferably, at least 10 xcexcm and at most 30 xcexcm.
When the diameter of the droplet discharge nozzles is smaller than 10 xcexcm, a general spacer with a diameter of about 2 to 10 xcexcm will clog in the nozzles and a desired number of spacers in a droplet cannot be stably emitted. On the other hand, when the diameter of the nozzles is larger than 100 xcexcm, the droplet does not become a perfect circle but a circle with a tail and adjacent droplets overlap due to excessive fluid volume, thus increasing probability that spacers are not arranged in desired positions.
The diameter of the droplet discharge nozzles is preferably at least twice as large as the diameter of the spacers. This is because if the diameter of the nozzles is smaller than twice the diameter of the spacers, the spacers may clog the nozzles or increase the variation in the number of spacers arranged in fixed points.
Also, the manufacturing method may further include the steps of forming a closed-frame-shaped seal member in the region in the surface of one of the pair of substrates; dropping the liquid crystal in the region enclosed with the seal member on the substrate having the seal member; and bonding the substrate having the seal member and the other substrate.
According to the manufacturing method, a liquid crystal is not injected by a vacuum injection method or the like after the substrates have been bonded together, but the liquid crystal is dropped on one of substrates before the substrates are bonded together and then the substrate is bonded to the other substrate. The use of the method allows not only the spacers but also the liquid crystal to receive the pressure during the bonding of the substrates, thus decreasing the number of spacers as compared with the conventional liquid crystal devices having an inlet. In other words, since the liquid crystal acts to receive part of the bonding pressure, the liquid crystal device with less spacers can bear the bonding pressure, thus keeping an even substrate spacing.
In the step of dropping the spacer dispersion liquid on the substrate, the droplet may be dropped at a spacing larger than the diameter of the droplet dropped on the substrate. The principle of arranging the spacers in fixed points by the droplet discharge method is as follows. After droplets containing spacers have been dropped in certain positions on a substrate, a solvent is evaporated. At that time, as the solvent evaporates gradually from the periphery of the droplets to decrease the center of each droplet, also the spacers gather at the center, so that the spacers are arranged in the center of the droplet. Accordingly, it is important that the droplets dropped on the substrate exist independently. Therefore, it is preferable to drop the droplets at a spacing larger than the diameter of the droplets dropped on the substrate. The reason is that if the droplets are connected together, the spacers will be positioned unstably, thus not necessarily being positioned at the center of each droplet.
An electronic device according to a third exemplary embodiment of the invention includes the above liquid crystal device. Having the liquid crystal device according to the invention allows an electronic device having a display with high display quality.